The invention is directed to a method and to an apparatus for setting the sharpness of an optical imaging system by step-by-step adjustment of the distance between a subject and an objective until a maximum is achieved for the respectively calculated sharpness values of the objective.
Methods and apparatus for setting the sharpness of an optical imaging system .can be used everywhere that imaging systems must be focused with extreme precision to nearly two-dimensional surfaces, for example image originals. Over and above this, methods and apparatus can be particularly advantageously utilized when it is a matter of optimally setting a pre-set focusing condition in a focus re-correction.
Methods and apparatus for setting the sharpness of an optical imaging system and for calculating the focusing condition are already known in the greatest variety of applications and embodiments. Solutions have thus already been recited for the various problem areas (which derive from the type of subject that can be two-dimensional or three-dimensional and low in contrast or high in contrast), from the desired depth of field range, and from the chronological demands and the implementation of the method. German Patent 31 41 182 thus discloses an apparatus for defining the focusing condition of an optical imaging system that enables the identification of the focusing condition of the imaging system such that a stabilized identification of the focusing condition that is largely independent of brief-duration lens-to-image variations is assured. For this purpose a memory and evaluation circuit is proposed that, however, undertakes numerous steps and is directed to the specific problem.
It has already been proposed for the field of self-focusing microscopes to form the brightness difference of every picture element of a usually three-dimensional original with respect to its two neighboring points with the assistance of a sensor and to add up these brightness differences for all picture elements, to then subsequently adjust the distance between subject and objective and to again form the said sum in order to then select that distance at which the allocated sum is a maximum (German Published Application 33 40 647).